1. Technical Field
The invention relates to electric lamps and particularly to electric lamps used in vehicles. More particularly the invention is concerned with a polymer coating for a vehicle signal lamp.
2. Background Art
Amber vehicle lamp bulbs are commonly used as signal lamps in motor vehicles. Historically amber bulbs were made with a cadmium doped glass to produce the amber color. For environmental reasons, cadmium has become an unacceptable material. There is now a market need for an environmentally sound alternative. Various color coated lamps have been developed, and their initial color can be acceptable. Given the specified expected ambient operating conditions for a vehicle, the bulb surface may have a temperature ranging from xe2x88x9240 to 350 degrees Celsius, so durability is difficult to achieve. In fact, the color, or the adherence of the existing coatings, or both have not been particularly good over time. Elapsed time for an automotive signal lamp can appear to be relatively long, while in fact the actual xe2x80x9conxe2x80x9d time can be relatively short. A signal lamp may be on for only minutes in the day of a vehicle""s operation, so the apparent life of the lamp may appear to be a year or more, when in fact the lamp has only been on cumulatively for only a few tens or even several hundred hours or so. In longer use, known coatings have been found to peel, or turn into a dust that falls off the bulb. Similarly the color may fade. The lamp color then departs from the required specification. There is then a need for an amber bulb coating material that meets standard color specifications, and has a durable life.
A durable amber colored lamp may be formed from a lamp bulb having a coating formed from a silane, a clear silicone-polyester resin, a yellow iron oxide, and a yellow anthraquinone.